ipc/sem.c: move wake_up_process out of the spinlock section

The wake-up part of semtimedop() consists out of two steps:

- the right tasks must be identified.
- they must be woken up.

Right now, both steps run while the array spinlock is held.  This patch
reorders the code and moves the actual wake_up_process() behind the point
where the spinlock is dropped.

The code also moves setting sem->sem_otime to one place: It does not make
sense to set the last modify time multiple times.

[akpm@linux-foundation.org: repair kerneldoc]
[akpm@linux-foundation.org: fix uninitialised retval]
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Manfred Spraul 2010-05-26 14:43:41 -07:00 committed by Linus Torvalds
parent fd5db42254
commit 0a2b9d4c79

123
ipc/sem.c
View File

@ -381,7 +381,6 @@ static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops,
sop--;
}
sma->sem_otime = get_seconds();
return 0;
out_of_range:
@ -404,25 +403,51 @@ undo:
return result;
}
/*
* Wake up a process waiting on the sem queue with a given error.
* The queue is invalid (may not be accessed) after the function returns.
/** wake_up_sem_queue_prepare(q, error): Prepare wake-up
* @q: queue entry that must be signaled
* @error: Error value for the signal
*
* Prepare the wake-up of the queue entry q.
*/
static void wake_up_sem_queue(struct sem_queue *q, int error)
static void wake_up_sem_queue_prepare(struct list_head *pt,
struct sem_queue *q, int error)
{
/*
* Hold preempt off so that we don't get preempted and have the
* wakee busy-wait until we're scheduled back on. We're holding
* locks here so it may not strictly be needed, however if the
* locks become preemptible then this prevents such a problem.
*/
preempt_disable();
if (list_empty(pt)) {
/*
* Hold preempt off so that we don't get preempted and have the
* wakee busy-wait until we're scheduled back on.
*/
preempt_disable();
}
q->status = IN_WAKEUP;
wake_up_process(q->sleeper);
/* hands-off: q can disappear immediately after writing q->status. */
smp_wmb();
q->status = error;
preempt_enable();
q->pid = error;
list_add_tail(&q->simple_list, pt);
}
/**
* wake_up_sem_queue_do(pt) - do the actual wake-up
* @pt: list of tasks to be woken up
*
* Do the actual wake-up.
* The function is called without any locks held, thus the semaphore array
* could be destroyed already and the tasks can disappear as soon as the
* status is set to the actual return code.
*/
static void wake_up_sem_queue_do(struct list_head *pt)
{
struct sem_queue *q, *t;
int did_something;
did_something = !list_empty(pt);
list_for_each_entry_safe(q, t, pt, simple_list) {
wake_up_process(q->sleeper);
/* q can disappear immediately after writing q->status. */
smp_wmb();
q->status = q->pid;
}
if (did_something)
preempt_enable();
}
static void unlink_queue(struct sem_array *sma, struct sem_queue *q)
@ -502,17 +527,22 @@ static int check_restart(struct sem_array *sma, struct sem_queue *q)
* update_queue(sma, semnum): Look for tasks that can be completed.
* @sma: semaphore array.
* @semnum: semaphore that was modified.
* @pt: list head for the tasks that must be woken up.
*
* update_queue must be called after a semaphore in a semaphore array
* was modified. If multiple semaphore were modified, then @semnum
* must be set to -1.
* The tasks that must be woken up are added to @pt. The return code
* is stored in q->pid.
* The function return 1 if at least one semop was completed successfully.
*/
static void update_queue(struct sem_array *sma, int semnum)
static int update_queue(struct sem_array *sma, int semnum, struct list_head *pt)
{
struct sem_queue *q;
struct list_head *walk;
struct list_head *pending_list;
int offset;
int semop_completed = 0;
/* if there are complex operations around, then knowing the semaphore
* that was modified doesn't help us. Assume that multiple semaphores
@ -557,40 +587,55 @@ again:
unlink_queue(sma, q);
if (error)
if (error) {
restart = 0;
else
} else {
semop_completed = 1;
restart = check_restart(sma, q);
}
wake_up_sem_queue(q, error);
wake_up_sem_queue_prepare(pt, q, error);
if (restart)
goto again;
}
return semop_completed;
}
/** do_smart_update(sma, sops, nsops): Optimized update_queue
/**
* do_smart_update(sma, sops, nsops, otime, pt) - optimized update_queue
* @sma: semaphore array
* @sops: operations that were performed
* @nsops: number of operations
* @otime: force setting otime
* @pt: list head of the tasks that must be woken up.
*
* do_smart_update() does the required called to update_queue, based on the
* actual changes that were performed on the semaphore array.
* Note that the function does not do the actual wake-up: the caller is
* responsible for calling wake_up_sem_queue_do(@pt).
* It is safe to perform this call after dropping all locks.
*/
static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops)
static void do_smart_update(struct sem_array *sma, struct sembuf *sops, int nsops,
int otime, struct list_head *pt)
{
int i;
if (sma->complex_count || sops == NULL) {
update_queue(sma, -1);
return;
if (update_queue(sma, -1, pt))
otime = 1;
goto done;
}
for (i = 0; i < nsops; i++) {
if (sops[i].sem_op > 0 ||
(sops[i].sem_op < 0 &&
sma->sem_base[sops[i].sem_num].semval == 0))
update_queue(sma, sops[i].sem_num);
if (update_queue(sma, sops[i].sem_num, pt))
otime = 1;
}
done:
if (otime)
sma->sem_otime = get_seconds();
}
@ -656,6 +701,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
struct sem_undo *un, *tu;
struct sem_queue *q, *tq;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
struct list_head tasks;
/* Free the existing undo structures for this semaphore set. */
assert_spin_locked(&sma->sem_perm.lock);
@ -669,15 +715,17 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
}
/* Wake up all pending processes and let them fail with EIDRM. */
INIT_LIST_HEAD(&tasks);
list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
unlink_queue(sma, q);
wake_up_sem_queue(q, -EIDRM);
wake_up_sem_queue_prepare(&tasks, q, -EIDRM);
}
/* Remove the semaphore set from the IDR */
sem_rmid(ns, sma);
sem_unlock(sma);
wake_up_sem_queue_do(&tasks);
ns->used_sems -= sma->sem_nsems;
security_sem_free(sma);
ipc_rcu_putref(sma);
@ -799,11 +847,13 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
ushort fast_sem_io[SEMMSL_FAST];
ushort* sem_io = fast_sem_io;
int nsems;
struct list_head tasks;
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
INIT_LIST_HEAD(&tasks);
nsems = sma->sem_nsems;
err = -EACCES;
@ -891,7 +941,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
update_queue(sma, -1);
do_smart_update(sma, NULL, 0, 0, &tasks);
err = 0;
goto out_unlock;
}
@ -933,13 +983,15 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
curr->sempid = task_tgid_vnr(current);
sma->sem_ctime = get_seconds();
/* maybe some queued-up processes were waiting for this */
update_queue(sma, semnum);
do_smart_update(sma, NULL, 0, 0, &tasks);
err = 0;
goto out_unlock;
}
}
out_unlock:
sem_unlock(sma);
wake_up_sem_queue_do(&tasks);
out_free:
if(sem_io != fast_sem_io)
ipc_free(sem_io, sizeof(ushort)*nsems);
@ -1213,6 +1265,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
struct sem_queue queue;
unsigned long jiffies_left = 0;
struct ipc_namespace *ns;
struct list_head tasks;
ns = current->nsproxy->ipc_ns;
@ -1261,6 +1314,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
} else
un = NULL;
INIT_LIST_HEAD(&tasks);
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma)) {
if (un)
@ -1309,7 +1364,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
if (error <= 0) {
if (alter && error == 0)
do_smart_update(sma, sops, nsops);
do_smart_update(sma, sops, nsops, 1, &tasks);
goto out_unlock_free;
}
@ -1386,6 +1441,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
out_unlock_free:
sem_unlock(sma);
wake_up_sem_queue_do(&tasks);
out_free:
if(sops != fast_sops)
kfree(sops);
@ -1446,6 +1503,7 @@ void exit_sem(struct task_struct *tsk)
for (;;) {
struct sem_array *sma;
struct sem_undo *un;
struct list_head tasks;
int semid;
int i;
@ -1509,10 +1567,11 @@ void exit_sem(struct task_struct *tsk)
semaphore->sempid = task_tgid_vnr(current);
}
}
sma->sem_otime = get_seconds();
/* maybe some queued-up processes were waiting for this */
update_queue(sma, -1);
INIT_LIST_HEAD(&tasks);
do_smart_update(sma, NULL, 0, 1, &tasks);
sem_unlock(sma);
wake_up_sem_queue_do(&tasks);
call_rcu(&un->rcu, free_un);
}